This invention relates to a supplemental exposure system for a photographic camera. More particularly, it concerns a method and apparatus for achieving an evenly exposed final photograph in a situation wherein the photographic scene is non-uniformly illuminated by an artificial light source by pre-exposing the film to supplemental illumination having a non-uniform pattern which is the inverse of the artificial scene illumination.
A common problem encountered particularly by users of amateur photographic equipment using commercially available artificial lighting assemblies to illuminate the scenes to be photographed has been a non-uniform exposure of the resulting photographs. Such non-uniformity is predictable in that the intensity of the scene illumination with most commercially available artificial lighting assemblies is highest at the center of the scene and generally decreases with increasing distance away from the center. As a result, subjects in the scene which are located near its edges receive less light than subjects located near the center of the scene and, therefore, are darker than they should be in the resultant photograph.
Such a problem is encountered in still cameras utilizing flash cubes and linear flash arrays which typically combine photoflash lamps with reflectors to illuminate the scenes to be photographed as well as in motion picture cameras making use of movie light assemblies for illuminating the scene being photographed.
Those skilled in the photographic arts who have found such uneven scene illumination characteristics objectionable have provided photographic apparatus for use with such artificial lighting assemblies to improve their illumination distribution to a level of uniformity which they have considered acceptable for their particular purposes.
One such example is disclosed in U.S. Pat. No. DES. 218,863 issued to James M. Conner on Aug. 11, 1970, and entitled "Light Deflector for a Photographic Camera". The light deflector in this patent comprises a transparent plate having a plurality of elongated V-shaped grooves which are separated from one another at equal intervals along the side of the transparent plate which faces a flashcube and which operate to modify the light distribution of the flashcube to make it more uniform. While this deflector improves the uniformity of the illumination provided by the flashcube with which it is used, its particular arrangement operates to refract light from the flashcube in such a manner that the overall efficiency of the flashcube in combination with the deflector is reduced, thus reducing the maximum distance at which flash pictures may be taken using this combination.
Another example of an optical device for use with a flashcube is disclosed in U.S. Pat. No. 3,720,145 issued to Bruce K. Johnson, et al., on Mar. 13, 1973, and entitled "Portrait Camera Having Synchronized Flash Illumination Source". In this patent, a portrait camera is disclosed which has a Fresnel lens mounted in front of the flashcube to focus light from the flashcube to a relatively narrow and limited field angle substantially the same as that of the field of view of the camera. The Fresnel lens operates to generally reduce the angular extent of the flashcube's normal field coverage so that its light output is concentrated within the camera's field of view.
U.S. Pat. No. 4,204,269 to William T. Plummer entitled "Optical Element for Redistributing the Light Output of a Photoflash Lamp Assembly or the Like" offers still another light deflector configuration for attempting to solve the uneven illumination problem set forth hereinabove.